1. Field of the Invention
This invention relates to a process of making a mixed metal oxide catalyst containing oxides of molybdenum, bismuth, iron, cesium, and other metals for the production of unsaturated aldehydes from olefins, such as methacrolein by gas phase catalytic oxidation of isobutylene in the presence of air or another gas containing molecular oxygen.
2. Description of the Prior Art
Typically, the catalyst for oxidation of isobutylene to methacrolein is a mixed metal oxide prepared by mixing compounds containing the desired elements in a solution or a suspension and drying the resulting concentrate. Thereafter, the dried product is calcined. The calcined product may be ground or formed to a mesh size suitable for use. The prepared catalyst can be prepared with a specific surface area. The catalysts may be supported on a suitable carrier, such as silica, silica-containing materials, silicon carbide, alumina and the like, in order to improve the physical properties of the catalysts. Many methods of making catalysts for use in the production of acrolein or methacrolein by catalytic vapor phase oxidation of propylene or isobutylene have been disclosed.
U.S. Pat. No. 4,388,223 discloses a catalyst for conversion of unsaturated hydrocarbons into unsaturated aldehydes and nitrites. Example 18 discloses a catalyst prepared by dissolving ammonium paramolybdate, 85 wt. % phosphoric acid and colloidal silica LUDOX AS containing 40% of SiO2 and water, forming a mixture of fused nitrates and pouring it into the solution which is maintained at 80° C. under agitation. A precipitate forms and a 30% aqueous solution of NH4OH is gradually added to set the pH value to 5.5, followed by a heat treatment at 80° C. for 4 hours, while controlling the pH value to 5.5.
U.S. Pat. No. 4,166,808 discloses a catalyst of oxides of cobalt, molybdenum, bismuth and iron for oxidizing olefins to α,β-unsaturated aldehydes. In Example 1, cobalt nitrate hydrate, iron nitrate hydrate and bismuth nitrate hydrate (with concentrated nitric acid for promoting the dissolution of the bismuth nitrate) were separately dissolved in water, the three nitrate solutions were mixed, ammonium heptamolybdate was dissolved in water, the nitrate solution was slowly added to the heptamolybdate solution with strong agitation to form a suspension which was further agitated at room temperature during 30 minutes. The mixture was heated to 80° C. in order to evaporate the water.
U.S. Pat. No. 4,151,117 discloses a supported catalyst of oxides of antimony, tin, tellurium, arsenic, bismuth or cadmium, iron or cobalt and molybdenum or tungsten for preparation of unsaturated acids, nitriles and aldehydes by oxidation. In Examples 1, 3, 5 and 7 agitation of the thick slurry formed by the catalyst components continues until the addition is complete and through raising the temperature to strip water off to form a thick paste.
U.S. Pat. No. 3,984,477 discloses a catalyst of molybdenum, bismuth and iron, nickel or cobalt. Separate solutions of ammonium molybdate and ethylenediamine-tetraacetic acid dissolved under heating in silica sol and of ferric nitrate, bismuth nitrate and potassium nitrate dissolved under heating in nitric acid-acidified silica sol were formed and mixed. The liquid mixture was heated and concentrated under agitation to form a slurry which was dried and heated to decompose the nitrates.
Prior art discloses different methods of making mixed metal oxide catalysts which contain molybdenum, bismuth, iron, cesium and other metals for the production of methacrolein. The advantages of a particular method of making or order of addition wherein the reaction slurry is aged or digested for a period of time with controlled agitation has not been disclosed.